THE GENUS COLOBOCENTROTUS. 19 
Figs. 9-11 are drawings of the characteristic stout elliptical radioles of 
P. atrata, rounded or slightly pointed at the extremity, taken from the 
ambitus where they form a ring at the base of the pavement of polygonal 
radioles extending from the abactinal side of the ambitus to the apex. The 
ambital radioles are from 15 to 20 mm. in length, and of a dark violet color, 
almost black on the upper side; on the actinal side the color of the spines 
is yellowish or light brown. These large radioles are finely striated, of a 
dark violet, with a well-marked milled ring. Blainville writes “d’un violet 
fongé presque noir.” 
Figs. 12-14 are views of short triangular radioles from the ambitus which 
form a part of the abactinal polygonal pavement of the test; they are taken 
from the left posterior interambulacrum. 
Figs. 15-17, views of a somewhat mushroom-shaped hexagonal or polygonal 
radiole taken from the abactinal side of the ambitus, from the right posterior 
ambulacrum. 
Figs. 18-20 and figs. 21-23 are polygonal radioles taken from the right 
anterior interambulacrum from the abactinal side of the ambitus; and figs. 
24, 25 is a similar radiole taken from the right posterior interambulacrum. 
Figs. 26-28, drawings of a low mushroom-shaped asymmetrical polygonal 
radiole taken from half way between the ambitus and the abactinal system. 
Figs. 29-31 is an irregularly hexagonal radiole taken from the genital 
plates; fig. 32 is a radiole taken from the madreporic genital; and fig. 33 
represents a miliary spine hidden by the large pavement of abactinal primary 
radioles. 
It will be seen on examining the figures of radioles given on Piate 23 that, 
with the exception of the spines of the actinal side and of the miliary spines, 
all the radioles are asymmetrical. 
The striking difference between the radioles of Podophora pedifera and 
those of Podophora atrata is well shown on comparing Pl. 11, figs. 11-13; 
14-16; 17, 18; 20-21; 22-24; 25-27; 28-30; 31-33 with Plate 23, figs. 7-8; 9- 
11; 12-14; 15-17; 18-20; 21-23; 26-28; 29-31. The most marked differences 
are in those of the ambital radioles (compare PI. 11, figs. 17-13 with Pl. 23, 
figs. 9-11). 
Podophora pedifera Agass. 
Plates 1; 3°, figs. 1-4; 4-16, figs. 1-8; 31, figs. 1-4. 
This species was figured in the Revision of the Echini (PI. IIT, fig. 3), 
under the name of Colobocentrotus atratus, and noted as having been collected 
